1. Field of the Invention
The present invention relates to a fuel cell including an electrolyte electrode assembly, and first and second separators for sandwiching the electrolyte electrode assembly. The electrolyte electrode assembly includes a pair of electrodes and an electrolyte interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which comprises two electrodes (anode and cathode) and an electrolyte membrane interposed between the electrodes. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is interposed between separators. The membrane electrode assembly and the separators make up a unit of a fuel cell (unit cell) for generating electricity.
In the fuel cell, a fuel gas (reactant gas) such as a gas chiefly containing hydrogen (hydrogen-containing gas) is supplied to the anode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions (protons) and electrons. The hydrogen ions move toward the cathode through the electrolyte, and the electrons flow through an external circuit to the cathode, creating a DC electric current. A gas chiefly containing oxygen (oxygen-containing gas) or air is supplied to the cathode. At the cathode, the hydrogen ions from the anode combine with the electrons and oxygen to produce water.
Generally, several dozen to several hundred of fuel cells are stacked together to form a fuel cell stack. In assembling the fuel cell stack, knock pins are inserted into positioning holes formed in each of the fuel cells for positioning the fuel cells with accuracy. However, if the number of the fuel cells is large, it is difficult to insert the knock pins in the positioning holes, and assembling operation may not be performed efficiently. Positional displacement between components may occur undesirably, and the desired sealing performance may not be achieved.
In an attempt to address the problem, Japanese patent publication No. 2000-12067 discloses a solid polymer electrolyte fuel cell 1 as shown in FIG. 12. The fuel cell 1 includes a unit cell 2 and separators 3a, 3b for sandwiching the unit cell 2. The unit cell 2 includes a solid polymer electrolyte membrane 2a, an anode 2b provided on one surface of the solid polymer electrolyte membrane 2a, and a cathode 2c provided on the other surface of the solid polymer electrolyte membrane 2a. 
Holes 4 extend through the fuel cell 1 in a stacking direction of the fuel cell 1 for inserting holding pins 6. The separator 3b has openings 5 for inserting snap rings 7. The holding pin 6 has a snap ring attachment groove 6a. The holding pin 6 is inserted into the hole 4, the snap ring 7 is inserted into the opening 5, and the snap ring 7 is fitted to the snap ring attachment groove 6a. At one end of the holding pin 6, a chamfered tip 6b is formed. At the other end of the holding pin 6, a hole 6c for inserting the tip 6b of another holding pin 6 is formed.
As described above, in the system of the fuel cell 1, the holding pin 6 is inserted into the hole 4, and the snap ring 7 is inserted into the opening 5. The snap ring 7 is fitted to the snap ring attachment groove 6a for tightening the fuel cell 1.
Thus, the tip 6b of the holding pin 6 projecting from the outer surface of the separator 3b is fitted to the hole 6c of another holding pin 6 which tightens another fuel cell 1. In this manner, the adjacent fuel cells 1 are stacked in alignment with each other.
According to the disclosure of Japanese patent publication No. 2000-12067, a plurality of the holding pins 6 need to be inserted into the holes 4 for each of the unit cells 2. Further, the snap ring 7 needs to be fitted to each of the holding pins 6. Thus, when a large number of unit cells 2 are stacked together, assembling operation of the fuel cell 1 is considerably laborious, and can not be performed efficiently.
When the fuel cell 1 is assembled, the tip 6b of the holding pin 6 projects from the outer surface of the separator 3b. Thus, electrical leakage may occur from the tip 6b of the holding pin 6.